This project involves examination fo the effects of single and repeated exposures to NO2 and O3, two important ambient air pollutants, upon clearance defense mechanisms of the lung, using the rabbit as the animal model. The mechanisms are mucociliary transport in the tracheobronchial tree and macrophage-mediated clearance from the alveolar region. Clearance is studied in unsedated animals using radioactively tagged tracer aerosols. Effects of NO2 and O3 upon specific functional aspects of alveolar macrophages will also be examined and related to measured overall clearance patterns. This project will provide information on the role of NO2 and O3 in producing clearance dysfunction, which may be an early stage in the pathogenesis of chronic obstructive lung disease.